The present invention concerns a delivery system for the introduction and release of a self-expanding stent in a body vessel, the self-expanding stent having a hollow cylindrical body and a proximal and a distal end, in which at least the proximal end has projecting loops pointing alternately in the proximal and distal direction, the loops having shoulders and straight sections.
Vascular stents, also called endovascular stents, are introduced into vessels to maintain patency, and are described in detail in the prior art. For example, vascular stent grafts can be introduced into damaged or occluded vessels to replace the vessel walls at the damaged or occluded points. A stent graft for this purpose has both a framework, which is usually made of wire, and a coating of biocompatible material.
Stents known from the prior art are, for example, used in vessels whose walls are thinned or thickened by disease or injury and which require support for that reason.
Many stents represent self-expanding stent systems which are introduced into the vessel in a compressed state and which are allowed to expand by removal of compressive structures. Such self-expanding stents must, therefore, contain an elastic material which can expand outwards, i.e., radially, as soon as force exerted to compress the material, e.g., a sleeve, is removed. Preferably, Nitinol is used, which can also have shape-memory properties, for this purpose. The framework of the stent is made of this material and preferably has a tubular structure, which usually has a slightly larger diameter than the vessel into which it is to be implanted.
The introduction and implantation of a stent or stent graft is generally carried out using a delivery system which has two tubular structures, namely an inner piston and an outer sleeve which can be moved axially with respect to one another. The stent is placed inside the distal end of the outer sleeve in a compressed state and is introduced into the vessel in this state. After placing the stent in the desired position, the piston is usually kept stationary, whereas the sleeve of the delivery system is drawn back, releasing the stent. Because of stop contact with the piston, the stent cannot move in the direction of the withdrawn sleeve when it is removed. The stent unfolds because of its self-expanding properties and presses against the vessel walls.
In the prior art, the end of the stent placed closer to the heart is usually designated as the proximal end whereas the end of the stent further away from the heart is designated as the distal end. In contrast, the designation of the ends of the delivery system as distal and proximal is such that the end closer to the operator is designated proximal and the other end further away from the operator is designated distal.
The proximal end of the stent or stent graft is typically designed such that the stent is mainly fixed to the vessel wall by this end. This is intended to prevent movement of the stent after its introduction in the vessel. The ends of the stent have spring components which form meandering encircling projecting loops or pointed arches which expand radially after their release and act as components for fixation to the vessel wall. In the expanded state, the proximal end with these fixation components or projecting loops/pointed arches usually has a larger diameter than the vessel into which the stent is introduced, precisely so that the projecting loops/pointed arches on the proximal end of the stent at least come into firm contact with the vessel walls and can become anchored there. For this reason, these projecting loops/pointed arches on the proximal end of the stent must be squeezed or compressed to introduce the stent and must be secured in the delivery system in such a way that they can be released.
In the case of many stents known from the prior art, both the remainder and the proximal end of the stent are compressed by the sleeve which holds the stent in the compressed state during introduction into the vessel.
The prior art also describes delivery systems which permit separate release of the proximal end of the stent from the rest of the stent.
A frequent problem in this regard is that it is necessary when introducing the system and the stent to withdraw the system slightly before expansion, as the stent or system was pushed too far forwards in the vessel. During this withdrawal, many stents and delivery systems in the prior art have the disadvantage that the projecting loops in the proximal end of the stent become caught in the vessel wall.